1. Field of the Invention
The present invention relates to an optical positional deviation detecting apparatus used for optically detecting a positional deviation (an alignment positional deviation) of a second mark (e.g., a resist mark) with respect to a first mark (e.g., a base mark) of a measurement mark (an alignment mark) formed on a substrate to be inspected such as a semiconductor wafer etc. in a photolithography manufacturing process etc. of a semiconductor wafer.
2. Related Background Art
A resist pattern is formed on a wafer at some separate stages in a photolithography manufacturing process defined as one of processes of manufacturing a semiconductor chip. To be specific, a predetermined resist pattern is formed in alignment on an already-formed pattern (which is called a base pattern) at each stage. It is, however, required at every stage that a positional deviation in alignment of the resist pattern with respect to the base pattern be detected and measured. There has hitherto been known an apparatus for detecting this positional deviation in alignment (see, for example, Japanese Patent Application Laid-Open No. 2000-77295). The measurement of the positional deviation in alignment, in which a measurement mark is configured by forming a resist mark on a base mark formed on the substrate when forming the resist pattern, involves the use of an optical positional deviation detecting apparatus (an alignment positional deviation detecting apparatus). In this optical positional deviation detecting apparatus, the measurement mark is irradiated with beams of irradiation, a CCD camera etc. photographs an image of the measurement mark from the reflected beams therefrom, then the photographed image is subjected to image processing, and a positional deviation quantity in alignment of the resist mark with respect to the base mark is measured.
By the way, in the case of optically measuring the positional deviation in alignment as described above, it is inevitable that an optical aberration occurs in a measurement optical system (including, namely, an irradiation optical system for irradiating the measurement mark with the beams of irradiation, and a converging optical system for converging the reflected beams from the measurement mark to form an image of this measurement mark). If this kind of aberration, particularly, an aberration that is rotationally asymmetric with respect to the optical axis exists in a measurement image field area, there occurs a measurement error TIS (Tool Induced Shift) of a measurement value of the alignment positional deviation. A quantity of the rotationally asymmetric aberration, which may be a factor of causing the measurement error TIS, changes depending on the measurement image field area. It is therefore required to set such a measurement image field area that the quantity of the rotationally asymmetric aberration is minimized.
As for the measurement image field area, in terms of the measurement error, an optimum image field area might differ depending on elements of the measurement mark (for instance, a height of the resist mark of the measurement mark, a height or depth of the base, a reflectivity, a size and so forth). Hence, even if in the same measurement optical system, it is required that the image field area be adjusted optimal with respect to each of many elements of the measurement mark, and the problem is that the adjustment of the image field area is difficult and time-consuming.